Hybridization and climate change in Alpine orchids

Hybridization is common in flowering plants, yet parental species are usually maintained. Gymnadenia orchids hybridize (Hedrén et al 2018), and hybrids occur in limited frequencies where parental species are found in abundance, suggesting the presence of strong reproductive isolation between the parents. The advent of novel genetic techniques and digitized historical data, as well as our increasing understanding of the effects of climate change on Alpine plants (Geppert et al 2020) makes this the right time to begin studying reproductive isolation and response to climate change in this diverse and charismatic group of flowering plants.

We hypothesize that hybrid orchids are rare due to the presence of multiple barriers between their parent species. The level of infertility seen in pilot studies suggests that hybrids may be the result of initial crossing between parent species only. Aims (1) and (2) address these hypotheses by determining hybrid ancestry and surveying multiple reproductive isolating barriers.

Aim (3) addresses temporal barriers specifically. Here, we hypothesize that flowering time will be sensitive to local climate conditions and that this will be reflected in historical data. Furthermore, we expect that this sensitivity may differ between species, leading to temporal barriers preventing hybridization.

Aim 1: Determine the ancestry of hybrid orchids

Using existing and new field collections, the student will genotype hybrids using the Orchidaceae963 kit (Eserman et al 2021) and use these data to determine hybrid ancestry using HYBRIDCHECK software (Ward & Van Oosterhout 2015). This will give the student experience in DNA library preparation and sequence analysis.

Aim 2: Understand reproductive isolation between parent species

Which barriers contribute to isolation between parent species, yet allow some hybrid formation? The student will study several barriers - prezygotic (temporal and pollinator isolation) and postzygotic (hybrid seed set/fertility) to address this, giving the student experience with botanical and entomological skills as well as evolutionary concepts.

Aim 3: Understand the effect of Alpine climate change on Gymnadenia

Observations have shown that species differ in their temporal isolation between sites. These differences are likely driven by local climate, and are thus extremely vulnerable to climate change. Alpine orchids appear to be lagging warming (Geppert et al 2020), making them particularly suitable models.

The student will visit sites multiple times over the season to determine flowering timing and its link with local climate conditions. Weather data (1863-) and orchid observations (1930-) will also be combined with herbarium records to study links between changing climatological conditions and orchid populations and flowering time.

Skills:

The student will gain skills in project management, fieldwork, and data collection and analysis. Should fieldwork fail, the student can rely on previously collected and historical data for all Aims. The student will be given mentoring on manuscript writing and outreach.

Byers will contribute training in fieldwork and associated analyses; Van Oosterhout will contribute training in genetic analysis of hybrids; and Coen will contribute training in species maintenance and reproductive isolation. The student will be hosted in the recently established Byers group, and will be the lead on all Aims.